This invention relates to metal organic chemical vapor deposition (MOCVD) deposition of inter layer metal conductors in integrated circuit processing, and specifically, to a method of deposition of a copper inter layer having good adhesion and trench filling characteristics.
There is a need to mass produce copper metal thin film for applications in the electronic industry. Those of ordinary skill in the art are aware of various laboratory methods of copper metal thin film depositions, including the use of various copper precursors, such as Cu(C5H5)(PR3), where R=methyl, ethyl, or butyl; Cu(hfac)(CH3Cxe2x89xa1CCH3), where hfac=hexafluoroacetylacetonate; and Cu(hfac)(tmvs), where tmvs=trimethylvinylsilane. Additionally, the use of various deposition techniques have been described.
To mass produce copper thin films, however, the laboratory methods must be adapted for commercial production. For instance, Cu(C5H5)(PR3) is not a good source for commercial copper chemical vapor deposition (CVD) processing because the carbon and phosphorus contaminate the copper thin film. Additionally, the cost of Cu(hfac)(tmvs) and Cu(hfac)(alkene) precursors is prohibitively high. Further, none of the known processes provide for a rapid CVD of pure, contaminate-free, copper. In the prior art, rapid deposition of copper thin films is achieved using a variety of copper precursors, however, the deposited copper thin films have poor adhesive qualities when applied to metal and/or metal nitride substrates, and such prior art rapid deposition may result in an unacceptably high resistance.
The use of water in CVD of copper is a well known expedient to improve adhesion, wherein a method of adding water vapor to Cu(hfac)(tmvs) improves the deposition rate of copper and increases the resistivity of the deposited copper thin films. The deposition rate of the copper is improved, but the resistivity of the deposited copper is poor.
The use of copper CVD precursors frequently results in the contamination of the resultant copper layer by interfacial carbon fluorine, which is found in copper precursors, such as CupraSelect and similar precursors. Such contamination results in poor adhesion of the deposited copper thin films to the underlying barrier metals. The interfacial contamination is a major obstacle to achieving good adhesion and adequate trench filling.
Because of copper""s low resistivity (1.7 xcexcxcexa9-cm) and high electromigration resistance, there has been a great interest in CVD of copper metal thin films. A copper metal thin film is considered the ideal material for use as the metal interconnections in integrated circuit devices.
However, the adhesion of a copper thin film on a metal nitride substrate is difficult to achieve, and generally results in a film exhibiting poor adhesive qualities and conductivity less than that of pure copper. A copper interconnect line is formed by depositing copper onto either of a dual damascene or single damascene trench, wherein the trench is lined with a barrier metal, such as a metal nitride, i.e., titanium nitride or tantalum nitride. The copper interconnect lines are delineated, typically by chemical mechanical polishing (CMP).
Deposition methods may include physical vapor deposition (PVD), metal organic chemical vapor deposition (MOCVD) and electrochemical deposition (ECD), however, PVD has poor step coverage, and ECD requires the initial deposition of a copper seed layer, which, of course, must be deposited by PVD or MOCVD. Because of the poor step coverage of the PVD technique, PVD is not suitable for applications where very narrow, ie., less than 100 nm, trenches are used to form the interconnects. MOCVD is more suited to deposition of copper in deep sub-micron trench/via copper fillings, and for providing the seed layer for ECD, however, the known MOCVD processes do not produce copper layers which have adequate adhesion between the copper layer and a metal barrier layer, such as a nitride layer. One solution is to use flash PVD to form a very thin seed layer prior to CVD or MOCVD, or to add a small amount of silicon to the barrier metal nitride compounds. While such processes provide adequate adhesion and conductivity characteristics for the copper layer, the process complexity is greatly increased, resulting in higher production costs and less throughput, and may increase the barrier metal-to-copper contact resistance.
Copper precursor composition has been modified in an attempt to improve the copper thin film adhesion. CupraSelect (Cu(hfac)(tmvs), or CupraSelect Blend (Cu(hfac)(tmvs)+H(hfac).2H2O) are precursors which have been found to improve the adhesion of copper thin films on a TiN substrate, however, such precursors have not demonstrated improved adhesion on a TaN substrate.
U.S. Pat. No. 5,322,712, to Norman et al., granted Jun. 21, 1994, for Process for Improved Quality of CVD Copper Films, describes introduction of an organometallic copper precursor and a complex copper vapor, or hydrate, of a volatile ligand.
U.S. Pat. No. 5,744,192, to Nguyen et al., granted Apr. 28, 1998, for Method of Using Water Vapor to Increase the Conductivity of Copper Deposited with Cu(hfac)(tmvs), describes use of 0.3% to 3% H2O to increase conductivity of a copper layer.
A method of forming a copper thin film on an integrated circuit substrate having a nitride component includes preparing the substrate; treating the substrate prior to copper deposition; depositing copper during a very short duration copper deposition step lasting between about 10 seconds to 40 seconds; baking the substrate and the deposited copper for between about one minute to ten minutes at a temperature greater than 385xc2x0 C.; and depositing copper during a long duration copper deposition step to deposit copper to the required thickness.
It is an object of the invention to provide a process for forming interlayer metal conductors in integrated circuits.
Another object of the invention is to provide copper interconnects which are highly adhesive to nitride substrates.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.